Apparatus for defrosting lowtemperature cooling coils



Aug. 25, 1953 E. KOHLSTEDT 2,649,695

APPARATUS FOR DEFROSTING LOW-TEMPERATURE COOLING COILS Filed April 10, 1950 Patented Aug. 25 1953 UNITED "STATES PATENr OFFICE" APPARATUS FOR nsraos'rmc Low- TEMPERATURE COOLING COILS Edwin Kohlstcdt, Alta, Iowa Application April 10, 1950, Serial No. 154,924

1 ,My invention is concerned with low temperature cooling coils of fan type cooling units. Specifically my invention is a method of defrosting or removing the frozen moistur from said coils when it collects thereon during normal operation.' g The use of mechanical refrigeration has become widespread. As a result, many improvements have been achieved and have given u a type of food storage heretofore impossible. These cold storage units have drawbacks, however, not the-least of which is the decrease in efficiency incurred by an accumulation of moisture on the cooling coils in the form of frost or ice. In the fan type cooler units, to which my invention particularly relates, a relatively great number of coolant carrying tubes or pipes are arranged in a box-like housing structure. These coolant carrying pipes aresituated in a parallel spaced apart relationship in respect to each other. Through the pipes a standard coolant of some form is circulated in operative relationship to a standard heat exchanger unit. At one end of the box frame is a large fan or blower that causes a stream of air to flow through the area in which the coolant carrying pipes are arranged. It is this stream of air, cooled by contact with the coolant carrying pipes that is th cooling agent for the storage room or the like. In order to insure that the air passing over the cooling unit will contact a sufiicient number of pipes to effect the desired reduction in temperature, the cooling coils are rather close together. Because of the relatively restricted air passageway between these numerous closely arranged pipes, any collection of frosted or frozen moisture on them tends to reduce noticeably the space available for a quantity of air to flow through the unit. It is possible that the air flow could be almost entirely out off if the accumulation of frosted or frozen moisture were allowed to getout of hand.

The situation just described is further aggravated by the fact that a series of fins or battles are usually arranged to further divide the space occupied by the main body'of the coolant carryingtubes. These fins are usually of some conducting metal to guide the air stream and further distribute the cooling effect of the cooling medium in the pipes. While these baffles are effective for this purpose, they also further re-- duce the air passageway. They, therefore, fur-;

ther promote the reduced efiiciency of the machine when frozen moisture collects because they ofier still further area for the formation of this snow and ice. It should be rather clear,

therefore, that it is very important to keep ac- 2 Claims. (01 62-4) passed over the coils dependent upon the quantity of air to be'cooled which is more or less fixed, the number of cooling coils which is fixed, and the temperature of the surface of the cooling units contacted by the air passing over them, an insulator around these pipes causes a drop in efliciency. The temperature inside the coils must be maintained at a low value for a longer period of time to produce the same amount of cooling since the insulator as well as the cooling air stream must be reduced in temperature. Since the accumulated moisture in a frozen condition acts as an insulator for temperatures below its own, its presence on the cooling coils will be highly undesirable. Here, then, is another pctent reason for reducing the amount of accumulated frozen moisture.

Until recently, the defrosting of coils in the fan type refrigerating systems has been accomplished by merely shutting down the system and allowing the temperature around the coils to rise naturally to a degree that would cause the accumulated ice and frost to melt. This technique is obviously slow. It is important, of course, to reduce the time necessary for removing this moisture if possible. It is obviously highly desirable to have the cooler ready to cool the air in the storage room at any time and short of this ideal as large a percentage of the total time as possible. Some at empts have been made to speed up the removal of frozen moisture with heating elements of one sort or another. In general however, it may be said that the known units for and method of heating these coils to defrost them is not entirely satisfactory. To date the technique used is that of incorporating a heating element in or closely associated with the entire length of the coolant carrying tubes. While the known forms of construction provide units that will remove accumulated frozen moisture, they have a definite disadvantage. tube to remove moisture the element itself becomes warm. When the moisture has been melted, the heating element is still warm. Somework of the cooling unit must be used, therefore, to reduce the temperature of the heating element before any effective cooling of the air stream may be started. In at least some of these units furthermore the coolant in the tubes is not removed during the defrosting process. It also, therefore, must be re-cooled before anyrefrigcrating is started. It is clear that the prior art leaves something to' be desired in the Way of quick, efiicient removal of frost and ice accumulations from cooling coils.

In view of these difficulties, it is the principal object of my invention to provide a method of removing the accumulation of frozen water from the cooling coils of a low temperature cooling system, i

It is a further object of my invention to provide a method of removing accumulated frozen moisture from the cooling coils of a mechanical re- In heating the;

frigerating system without heating the cooling medium used therein.

It is still a further object of my invention to provide a method of heating cooling coils of fan type refrigerating system that interposes. no part of the heating element in the path of the blower duct. It is yet another object of my invention to provide a method of heating the cooling coils of a fan type cooling system in which the heating medium is separably associated with the cooling coils.

These and other objects will be apparent to those skilled in the art.

My method consists of the technique described in the specification and diagrammatically il1ustrated in the accompanying drawing in which the figure is a perspective diagrammatic view of an application of my method to a mechanical re frigerating system with portions cut away to illustrate more fully my invention.

Referring to the drawings the numeral designates the box-like main frame or air passageway. The coolant carrying pipes designated H are arranged back and forth across the passageway. l2 designates the conducting fins which aid in supplying broad cooled surfaces to contact the air to be cooled. Conduit I3 carries the cooled compressed coolant from condenser coils [4 to the cooling coils. Solenoid valve I5 is normally open to permit this flow. Conduit i6 is a return from coils II to compresser I! that is driven by motor [8. A fan [9, here shown driven by a separate motor 20, circulates cooling air across the condenser coils. In an actual installation motors I 3 and 20 are usually the same. So far I am merely laying the groundwork for my invention which I will now describe.

It is my purpose to remove quickly the accumulated frost and ice from the coils I I by bringing a heated substance into contact with the said coils. Illustratively I show liquid tieht tanks 2! and 2?. enclosing the area around the ends of the coil loops "3. A fraction 0 a large blower or fan 2 is shown in the broken away area in the main body section I0. It is this fan that actually circulates the cooling air across the coils II. The tops of the tanks 2| and-22 are connected by a conduit 25 to pump 26. Reservoir 21 is connected to the pump by tube 28. Return line 29 from tanks 21 and 22 allows fluid to flow back into the reservoir. A source of heat such as gas flame 30 is located under the reservoir to heat its contents when solenoid operated valve 3| is energized. The source of heat element 33 may also be an electric heating element, of course. Motor 32 drives the pump when necessary. The sequence of operation of all the periodically operating defrosting equipment is controlled by timer switch 33. Check valve 34 permits air to enter the heating tank system when the defrosting cycle is ended.

In operation the sequence of events in the illustrative mechanism embodying my method is as follows: The timer 33 actuates solenoid valve 3| sometime before the actual defrosting cycle is to commence to heat up the fluid in reservior 21, This fluid may be either water or oil. When the heating fluid has had time to become warm, a second contact in timer 33 actuates solenoid valve (5 to close conduit l3 and prevent any additional cooling medium from being introduced into the cooling coils. Compressor l'l continues to withdraw coolant from the system, however, until the pressure in the cooling coils becomes so low that a low pressure cut-out switch, that reservoir 21 into tanks 2| and 22.

is standard equipment in such systems, shuts off the compressor motor l8 and fan motor 20. At this point, timer 33 starts motor 32 that in turn actuates pump 26 which forces heated liquid from The heated fluid surrounding the ends of the cooling coils as it does quickly raises the temperature of coils H to a point that rapidly melts off any accumulated frost or ice. It should be mentioned at this point also that fan 24 must be stopped during the defrosting process. This is especially advantageous in those cooling systems of the fan type where the fan and coils are situated outside the room that is being refrigerated. It will be noted that since the cooling medium was withdrawn before the heating of the coils was begun, little or no heat is transferred to the cooling substance. What coolant does remain in the coils H however, is heated, and expanded therefore, to increase the pressure in the cooling system to cause the low pressure cut-out switch to turn on the cooling system again. Before the coolant system begins to operate again, however, the timer 33 has stopped motor 32 and the heated fluid drains out of tanks 2| and 22, to reservoir 21. Check valve 34 allows air to enter the system so that the fluid will drain quickly. Solenoid valve 15 is de-energized before the refrigerator mechanism is started, of course, so that coolant may be again introduced into coils II. The cycle is now complete and ready to start all over again when the predetermined moment is reached.

Some chan' es may be made in my method of defrosting the cooling coils without departing from the real spirit and purpose of my invention, and it is my purpose to cover by my claims any mcdified forms of my technique which may be reasonably included within their scope.

I claim:

1. In a blower finned type refrigerating unit having cooling coils with portions thereof that extend beyond the fins; said refrigerating unit also equipped with a compressor, tanks surrounding the coil portions of said refrigerating unit that extend beyond the fins thereof, a valve in the cooling system of said blower finned type refrigerating unit between the compressor and cooling coils, a pump, a reservoir, conduits communicating between said reservoir, heatable fluid in said reservoir, said pump and said tanks making a closed circuit, means secured near said reservoir for heating its contents at times, and means for driving said pump at times.

2. The blower type refrigerating unit of claim 1 further characterized by a timed control unit connected to all of the parts of the blower finned type refrigerating unit to control their operation in the following sequence; starting said reservoir heating means, closing said valve, stopping said compressor, starting said pump driving means, and restarting the refrigerating mechanism after a predetermined time interval.

EDWIN KOHLSTEDT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,890,085 Hill Dec. 6, 1932 1,908,573 Sulzberger May 9, 1933 2,081,479 Fink May 25, 1937 2,400,168 Roach May 14, 1946 2,433,574 Newton 1 Dec. 20, 1947 2,524,568 Kritzer Oct. 3, 1950 2,526,032 La Porte Oct. 17, 1950 

